如何在PHP中加入多个MySQL查询

Question

i have a category tabale

parent_cat  cat_id title
0             1   fruit
0             2    vehicle
0             3    goods
1             4    sour
1             5    sweet
1             6    mixed
2             7    sedan
2             8     hatchback
2             9     car

and product table

offer_name parent_cat sub_cat
mango         1        4,6
maruti        2        7,8,9
apple         1        5,4

i want to join the table according the requested get parameter if ?title=fruit then i will get mango,apple and my sql query is

SELECT category.cat_id,category.title,product.parent_cat,product.offer_name 
FROM category, product 
WHERE category.cat_id=product.parent_cat 
AND category.title='fruit' --requested get variable

output is :  cat_id  title  parent_cat  offer_name
               1     fruit      1          mango
               1     fruit      1          apple

if ?title=sour then i will get mango,apple and my sql query is

SELECT * FROM product WHERE CONCAT(',' , sub_cat , ',') LIKE '%,4,%'

output is : offer_name parent_cat  sub_cat
                mango     1           4,6
                 apple    1           4,5

my question is how to convert sour which id is 4 in place of '%,4,%' .so that i can put the get variable over there.how to join like 1st mysql query

Answer 1

if a product belongs to multiple categories you should have multiple rows in your table. it`sa many to many relationship. and your sql should be SELECT * FROM product WHERE sub_cat in ( ... )

Answer 2

The answer is: you can't.

MySQL cannot deal with comma separated lists. You basically have two choices:

#1 Make two queries

Basically get the cat_id first and then do the second query as in your example. But then you don't avoid the LIKE '%,4,%' .

#2 Do it the relational database way.

As mentioned by user3642242 you have a many-to-many-relationship. Usually in SQL you would use another relationship table in this case. So you would have a category , product and category_product_relationship table. Your category_product_relationship table would then look like this:

category_id  product_id
1            1
1            3
2            2
...          ...

It means that the product table needs an index, which is a good idea anyway since SQL loves Primary Keys and is super fast with them.

You would then do a JOIN to query your products like so:

SELECT *
FROM category c
JOIN category_product_relationship r ON r.category_id = c.cat_id
JOIN product p ON p.id = r.product_id
WHERE c.title = 'sour'

(c, r and p are aliases)

You can then remove the parent_cat and sub_cat columns from your product table and handle all of that through the relationship table.

Answer 3

As others have suggested you should consider redesigning your database in a proper relational way. But it is possible to get what you are looking for with the following query:

SELECT offer_name, parent_cat, sub_cat FROM product JOIN
(SELECT cat_id FROM category WHERE title = 'sour') AS temp ON
CONCAT(',',sub_cat,',') LIKE CONCAT('%,',temp.cat_id,',%')